The cardiovascular system is the primary circulatory system of the human body. It’s main function is transport. It also provides protection against foreign substances. The arteries of this system generally carry blood from the chambers of the heart to the tissues of the body, while the veins carry blood from the tissues of the body to the chambers of the heart. The blood circulation is a two cycle system which involves both the pulmonary cycle and the systemic cycle. In the former, the pulmonary cycle, blood circulates from the heart to the lungs and back to the heart.

In simple organisms such as unicellular and one or two layer organisms, materials can be transferred among cells by simple processes of diffusion. However, in large organisms, a system is needed for the distribution and collection of materials. The circulatory system is used by the human body to carry substances. Some substances are collected from the body cells for elimination. The body also produces hormones which are the products of the endocrine glands.

Some of the liquids of the body are blood, lymph or cerebrospinal fluid. Some of the vessels of the body include the blood vessels and lymph vessels. Blood is composed of the following: plasma and formed elements. Plasma makes up about 55 percent of the total blood volume. Water is also a part of our body composition. It has an ample heat-carrying capacity. Along with dissolved salts, plasma proteins help to maintain the tonicity of the plasma. Fibrinogen is important to blood clotting. The percentage by volume of red blood cells in the blood is called haematocrit. Haemoglobin, a special protein, is found within red blood cell cytoplasm. The normal, mature red blood cell is a biconcave disc. White blood cells are another of the formed elements of the blood, they are also known as leucocytes. There are several types of white blood cells including neutrophils, monocytes, phagocytes and lymphocytes. Platelets are also another type of formed element in the blood.

The blood is the vehicle for the cardiovascular system; it is used to transport substances around the body. Oxygen in the air fills the alveolus of the lung and carbon dioxide is produced during metabolic oxidation within the individual cell.

The blood carries glucose and oxygen around the body. When the hormone epinephrine is secreted by the Adrenal Gland, it is delivered to all parts of the body by the cardiovascular system. In periods when much energy is required, the body can use its stores of fat as a source of energy.

Human beings in populations have a tendency to modify ecosystems that are existing for purposes centered around their own. They clear forests and grasslands for the growing of crops. They build their houses on what used to be farmlands, and they convert small towns into overcrowded cities. Human being populations continue to increase in size and so they require ever greater amounts of material good and energy input with each passing year. As each second goes y original organisms become fewer and fewer until eventually some ecosystems have been completely altered. If this type of progression continue what will remain will be human beings and their domesticated plants and animals were there were once diverse populations.

As human being populations increase more and more ecosystems are threatened. The destruction of world’s rain forests are of great concern. The destruction is due mainly to over logging. As years go by we are realizing even though slowly, that we are dependent on intact ecosystems and how they service us. A prominent example and a useful one, is the purpose and essence of our rain forests. They are absorb of carbon dioxide. This gas is a pollutant if allowed to build up in our atmosphere. If it is allowed to build up it effects are grave such as increasing our daily atmosphere temperature.

When human beings interfere by modifying existing ecosystems they are contributing to the reduction of biodiversity. The term biodiversity is defined as the total number of species, the variability of their genes, and the ecosystems in which they live. Species become extinct meaning they die, when such species is unable to successfully adapt to a change in their environmental conditions. A shocking example is that seaside development, pollution, and over fishing are causing valuable fin fishes to become commercially extinct. This means that those that remain are too few to justify the cost of catching them.

Human beings need to realize that we are totally dependent on other species for food, clothing, medicines, and various raw materials. There it shows we have no vision when we allow other species to become extinct. We should preserved ecosystems and the species living in them because that is how the human species will continue to survive.